The phenomenon of transformation of muscle into meat after slaughtering animals rests on glycogenolysis which results in the accumulation of lactic acid in the muscle fiber. The pH of the muscle decreases to reach values normally less than 6.
Now, it is observed for certain muscles that an anomaly exists in the acidification process after death, which is manifested by higher pH. These high-pH meats are recognizable by their deep red color, sometimes almost black, which justifies their being named as dark-cutting meat, or DFD meats (Dry, Firm, Dark).
This phenomenon of high-pH is explained particularly by a premature exhaustion of the stock of muscle glycogen before slaughter, which results in an insufficient lactic acid level and hence, an insufficient lowering of the pH: the latter is then greater than or equal to 6. The post-mortem biochemical reactions which arise therefrom are responsible for the mediocre quality of this meat.
In fact, apart from the color, the high-pH has other unfavorable consequences on the meat, such as considerable water retention capacity, mediocre organoleptic properties and especially poor preservation.
A very complete article, which appeared in the French publication RTVA, No. 177 - April, 1982, pages 5 to 20, analyzes the mechanisms of occurrence of dark-cutting meat, the factors of occurrence as well as the prevention of the risks of occurrence of these meats.
It is well established that dark-cutting meats are considered as defective and are subject to notable commercial depreciation. They represent therefore an economic problem prejudicial to the whole meat industry.
The exhaustion of the stock of glycogen, recognized as being at the origin of the occurrence of these dark-cutting meats, is principally due to stress and to the physical efforts of the animal before slaughter.
In fact, the accumulation of disturbances undergone by the animal from departure from the place of fattening to the slaughterhouse and in particular during loading, transportation and waiting in the slaughterhouse, constitute equally aggressions for the animal, which finds itself subjected to emotional disorders which are accompanied by hormone secretion (adrenalin) as well as to the unusual physical expenditure.
Thus, the handling and mixing of batches of animals during collection and transportation, which cause agitation of the animals, just as the diet during transportation and waiting in the slaughterhouse, contribute to depleting the glycogen reserves of the animal and hence to causing the phenomenon of high-pH meat.
In addition, it has been shown that certain species are more sensitive than others to the occurrence of this type of meat. On this subject, reference may be made to the publication which appeared in RTVA, July/August 1984, pages 10 to 16.
Besides the breed, other parameters such as the sex and age of the animals, their weight, their state of fattening, their origin, and the time of waiting in the slaughterhouse have been correlated with the level of occurrence of dark-cutting meats. A study of these parameters has thus been reported in RTVA, No. 85, January/ February 1983, pages 3 to 8.
These various studies have enabled preventive measures to be discovered against the occurrence of dark-cutting meats, which measures seek to control the extrinsic factors causing stress in the animal, and consequently, excessive consumption of muscular glycogen.
These measures consist particularly in not mixing the animals of diverse origin, of optimizing the conditions of unloading, reducing the transport time as well as the stalling at the abattoir.
However such measures, if they contribute to limiting the causes of the appearance of dark-cutting meat, are however far from enabling the disappearance of this phenomenon.
Chemical treatments have therefore also been proposed. Thus, H. Wichlacz, E. Grzeskowiak and K. Krzywicki, from the Meat and Fat Research Institute, Warsaw, Poland, have shown that, in the bull-calf, molasses solutions contribute to reestablishing the stock of muscle glycogen.
However, the results obtained are difficult to interpret, to the extent that the animals have also received hay. In addition, molasses solutions have the drawback of being extremely fermentable.
Trials of prevention of the occurrence of high pH-meat have also been carried out in 1985 by ITEB (Institut Technique de l'Elevage Bovin - France) by the contribution of energy either in the form of monopropylene glycol, distributed previously to the transportation of the animals, or in the form of lactoserum, distributed during the waiting in the slaughterhouse, to limit recourse to the muscle glycogen reserves.
Another publication (V.P.C. Vol 9 (3) June 88) dealing with the use of lactoserum for preventing the occurrence of high-pH meat in young bulls has clearly established that this product has a significant effect.
But lactoserum distribution is, according to the author, only justified if the bulls are maintained in the abattoir for at least 48 hours.
In addition, K. Kousgaard, of the Danish Meat Research Institute (EEC Seminar on the problem of Dark-cutting in Beef, 1987, Brussels) has proposed for young bulls kept in overnight lairages, a feed constituted principally of a mixture of sugar beet pulp, molasses and barley.
However, this treatment appears to be satisfactory only for animals which remain at least two nights in the slaughterhouse, which greatly limits its interest.
In addition, while providing a solid feed in the slaughterhouse is possible within the framework of an experiment, it is not easy to apply in practice, the installations not being designed to permit feeding of animals which are to be slaughtered.
J.M. McVeigh and P.V. Tarrant (Farm & Foods Research, 1983, 14, n.sup..degree. 2) studied propanolol, which is a beta adrenergic blocking agent already proposed by Ashmore et al (Journal of Animal Science, vol. 36, n.sup..degree. 1, 1973) to reduce the exhaustion of the glycogen stock in the sheep and the calf. In fact, this substance opposes the effect of adrenalin by fixation to the beta receptors of the cells of the muscle. However, in the experiment described by McVeigh et al, propanolol is not shown to be effective in the prevention of the occurrence of dark-cutting meat, the emotional stress which causes the secretion of adrenalin not being the principal cause of the drop in glycogen level, contrary to unusual physical activity.
Finally, P.V. Tarrant (Irish Journal of Food Science and Technology, 13, 1989) has established that the contribution of dexamethasone before stress, and of insulin and of glucose after stress, results in a hyperglycemia without reducing the consumption of muscle glycogen.
The majority of solutions proposed until now are therefore not satisfactory and/or accompanied by installation constraints and prohibitory times.
Now, Applicants have discovered that the frequency of occurrence of dark-cutting meat or of meat with high pH was, quite surprisingly and unexpectedly, very substantially reduced provided that an amount of sorbitol effective for reducing the frequency of occurrence of dark-cutting meat or of high-pH meat is administered, sometime before their slaughter, to animals destined for slaughter.
It is accordingly an object of the invention to provide a method enabling reduction in the occurrence of dark-cutting meat or of high-pH meat in animals, and in particular in ruminants.
It is also an object of the invention to provide a feed supplement for animals intended for the slaughter, enabling the occurrence of dark-cutting meat or of meat with a high pH to be significantly reduced in these animals.
Nothing in the prior art permitted those skilled in the art to imagine that sorbitol would have such an effective and rapid effect on the very particular phenomenon of dark-cutting meats or meats with a high-pH.
Sorbitol, known to be a regulator of bile and pancreatic functions in man, has indeed already been proposed for animal feed, but never has such an effect on the occurrence of dark-cutting meat been described or even suggested.
Thus, it may be noted that sorbitol has already been proposed in animal feed for the purpose of improving meat production or milk production.
French Pat. No. 2.447.152 filed by Applicants describes for example the use of sorbitol to improve the feeding of calves.
In the same way, U.S. Pat. No. 4,127,676 claims a fodder additive for ruminants, based on polyols, among which are particularly sorbitol, in order to increase meat production.
In addition, U.S. Pat. No. 2,876,157 describes the parenteral administration of sorbitol and of glucose in order to treat ketoses in ruminants.
Finally, in French Pat. No. 2.565.071, Applicants have proposed the use of sorbitol to increase the average daily weight gain of ruminants without a larger consumption of feedstuffs.